Sharp constants of approximation theory have attracted much attention of approximation analysts
for more than a century (see monographs
[1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]}, [8]} and references therein).
Our unified definition of the sharp constant (see (REF )) includes constants in
three major problems of approximation theory, such as, inequalities for approximating elements
(Problem A), approximation of individual elements (Problem B), and approximation on
classes of elements (Problem C).
